Generally, a noise component is included in a digital signal obtained from an image pickup device and an analog circuit accompanied therewith and an A/D converter of the image pickup device and, mainly, is classified into a fixed pattern noise and a random noise.
The fixed pattern noise is substantially caused by noises from the image pickup device, typically, a defect pixel.
The random noise is generated in the image pickup device and the analog circuit with a characteristic approximate to the white noise characteristic.
Japanese Unexamined Patent Application Publication No. 2001-157057 discloses one technology for adaptively reducing the noises depending on a signal level under the control of the frequency characteristic via filtering based on an amount N of noises which is estimated for a signal level D from a function [N=abcD] where reference symbols a, b, and c denote statically-given constant terms and the signal level D is a resultant value of the conversion into the concentration level.
Further, Japanese Unexamined Patent Application Publication No. 2002-57900 discloses another technology for reducing the noises without deterioration in original signals at the edge thereof by controlling an average number n of pixels for moving average which is used as a function [n=a/(Δ+b)] where reference symbol Δ denotes a differential Δ between a target pixel and an adjacent one thereof and reference symbols a and b denote statically-given constant terms and by using no moving average when the obtained differential Δ is a predetermined threshold or more. Further, the signal after the reduction of noises are recorded and stored via the compression using the frequency space of JPEG and MPEG and, in the replay operation, the compressed signals are decompressed.
Both the functions disclosed in Japanese Unexamined Patent Application Publication No. 2001-157057 and Japanese Unexamined Patent Application Publication No. 2002-57900 are defined in real space and the noises are reduced by using the functions in the real space. On the contrary, the signals are generally compressed/decompressed in the frequency space, independently of the noise reduction.
With the above-mentioned structure, the independent system processing of the noise reduction and the compression/decompression causes a problem against the low-cost structure of the image pickup system and the replay system for fast processing.
The fixedly-given constant terms in the above-mentioned functions do not correspond to the partial update of the system or the aging change, thereby causing the inflexibility. Further, the systems according to the technologies disclosed in Japanese Unexamined Patent Application Publication No. 2001-157057 and Japanese Unexamined Patent Application Publication No. 2002-57900 have a problem to enable the noise reduction only with the calculated constant terms for functions.
The present invention is devised in consideration of the above circumstances. It is one object of the present invention to provide an image pickup system and a replay system for fast obtaining a high-quality image with low costs.
Further, it is another object of the present invention to provide an image pickup system and a replay system for flexibly obtaining a high-quality image corresponding to various systems.